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Experimental investigation has been carried out for laser ignition and combustion of nanothermites based on aluminum and oxides of copper, bismuth and molybdenum. Ultrasonic mixing of nanosized powders was used to produce compositions. For thermite ignition, initiating laser pulse with a maximum intensity of 770 W/cm2 was generated by a laser diode with a wavelength of 808 nm. The ignition delay times, the minimum initiation energy density, and the average burning rate at various thermite densities and mass fractions of components were determined by recording the emission of radiation of the reaction products using a multichannel pyrometer jointly with a high-speed video camera. The effect of adding carbon black on the threshold parameters of a laser pulse was also studied. Based on the obtained results, certain assumptions were put forward with regard to the mechanism of nanothermites’ ignition by laser radiation and their burning. In particular, the assumptions were made on the two-stage process of the reaction initiation and jet burning mechanism of porous nanothermites.

Here, we have thoroughly studied the effect of chemistry of graphene derivatives on the composition of N-species after N-doping with the help of core-level spectroscopy techniques. The modulation of the N-species by tailoring the functionalization and atomic structure of graphene derivatives prior to chemical N-doping is experimentally demonstrated for the first time. The large extent of non-terminated or phenol-functionalized graphene edges is found to facilitate the formation of pyridinic nitrogen with its relative content exceeding 72%. In turn, the predominant decoration by the pyrazolic moieties is shown for the perforated and carboxyl-derived graphene layers. The thermal annealing at moderate temperatures of ca.345 °C is shown to equally readjust the composition of N-species in graphene derivatives regardless of their chemistry, nanostructure, and the initial distribution of the N-species. Further examination of N K-edge X-ray absorption spectra (XAS) pointed out that the oxidation of the graphene layer governs the manifestation of the π∗ resonances and configuration of the σ∗ resonance. As a result, a set of facile methods to synthesize graphene derivatives with the desired type of the embedded nitrogen species for the optoelectronic and catalytic applications are proposed and crucial features of their identification using core-level spectroscopy techniques are emphasized.

Silica particles containing large mesopores (5–25 nm in size) and micropores (0.6–2 nm in size) have been prepared by chemical etching of spherical micro- and mesoporous silica particles in an ammonia + water + hydrogen peroxide mixture. The specific surface area and pore volume of the particles are 510 m2/g and 0.8 cm3/g, respectively. Using capillary impregnation, we have synthesized Co3O4 (2–4 wt %) in pores of the particles. The composition and structure of the resultant materials have been studied. The Co3O4/SiO2 composite particles have been shown to be stable and exhibit catalytic activity for the CO oxidation process.

We report a new environmentally friendly and simple method to produce monolithic magnetic composites C/Ni nanoparticles (NiNPs) consisting of highly porous carbon matrix and well-separated Ni nanoparticles covered by graphite-like shells. The method is based on the carbonization of wood with addition of nickel nitrate and wood decomposition product (tar) as a binder. The specific structural features and magnetic properties of the C/NiNPs composites are systematically investigated. We have demonstrated the change in average size of NiNPs from ~ 9 to ~ 18 nm and in their magnetic character from superparamagnetic to ferromagnetic behavior by changing the pyrolysis temperature. The macroscopic magnetization 3.5 emu/g (38 emu/g(Ni)) of the obtained porous monolithic nanocomposites with small amount of nickel (8.8 wt.%) in low magnetic field and their ferromagnetic behavior at room temperature make them ideal candidates for use in applications involving magnetic separation (heterogeneous catalysis, adsorption of contaminants in aqueous media, etc.). The resulting maximum magnetization 38 emu/g(Ni) of carbon-encapsulated NiNPs is comparable and even somewhat exceeds that of similar core–shell Ni nanoparticles obtained by other methods. The fundamental question arises whether it is possible to achieve the magnetization for carbon-encapsulated NiNPs as that in the bulk Ni.

The results of structural studies of GaN nanowires containing screw dislocations are presented. It is found that the length of the Burgers vector of dislocations may reach 5 nm, i.e., exceed many times the c parameter of the gallium nitride unit cell. The formation of such dislocations leads in some cases to the occurrence of an ordered sequence of basal stacking faults with a period of 1.3–3.9 nm.

In the present paper, a new approach for detonation nanodiamond (DND) deagglomeration is proposed. DND agglomerates of the size from 20 to 200 nm have been exposed to wet sonication assisted oxidat...

One of the industrially scalable methods for the synthesis of diamond crystals is shock compression of graphite. The method includes shock compression of graphite with explosives (RDX). Typical siz...

Here, the synthesis of holey carbonylated (C-ny) graphene derivative and its application for gas sensing is demonstrated. The carbonylation of graphene oxide leads to the 3-fold increase in the concentration of carbonyl groups’ up to 9 at.% with a substantial elimination of other oxygen functionalities. Such a chemical modification is accompanied by the perforation of the graphene layer with the appearance of matrices of nanoscale holes, leading to corrugation of the layer and its sectioning into localized domains of the π-conjugated network. Combined with the predominant presence of carbonyls, granting the specificity in gas molecules adsorption, these features result in the enhanced gas sensing properties of C-ny graphene at room temperature with a selective response to NH3. Opposite chemiresistive response towards ammonia when compared to other analytes, such as ethanol, acetone, CO2, is demonstrated for the C-ny graphene layer both in humid and dry air background. Moreover, a selective discrimination of all of the studied analytes is further approached by employing a vector signal generated by C-ny multielectrode chip. Comparing the experimental results with the calculations performed in framework of density functional theory, we clarify the effect of partial charge transfer caused by water and ammonia adsorption on the chemiresistive response.

The impurity cluster formation in 64Zn+ ion hot-implanted and subsequently thermal-oxidized Si substrates are studied. After implantation on sample surface and in sample near-surface layer, the metallic Zn clusters with the average size near 200 nm on sample surface and the clusters with size about 20 nm in a sample body were created. After annealing at 700 °C, there was transformation from metal Zn clusters to its oxide form such as ZnO(core)/Zn2SiO4(shell) on a sample surface and conservation of the metallic Zn phase in a sample body. We propose an explanation of this phenomenon by temperature dependence of the oxygen molecules diffusion in silicon body and zinc atom opposite moving to the sample surface during annealing.

A structural study of graphene oxide complexes with detonation nanodiamonds (particle size 4–5 nm, positive surface potential) in aqueous suspensions by small-angle neutron scattering is reported. While the pure graphene oxide suspension exhibits a completely planar structure, the grafting of detonation nanodiamond particles results in a slightly curved surface of the graphene oxide flakes. The complexes “graphene oxide–detonation nanodiamonds” washed out from free detonation nanodiamonds show that the effective curvature of the graphene oxide plane is the result of binding of detonation nanodiamonds in the form of planar aggregates.

The mid-infrared (IR)-sensitive n/p-junction was fabricated on a p-doped silicon (Si) wafer via ultrashort laser n-type surface hyperdoping and high-temperature annealing. First, the n-type sulfur ...

The results of experimental studies are presented and the experience of operating the power supply of a continuous gas laser, which is based on a lithium–polymer storage battery without an intermediate voltage converter, is analyzed. The long-term (more than 4-year) operation of a high-voltage battery power supply as a component of a laser system with an open-circuit voltage of 7.76 kV, a load voltage of 6.1 kV, a load current of up to 250 A, a power higher than 1.5 MVA, and a stored energy of 550 MJ is demonstrated. The response time of the switch for disconnecting the load in the case of breakdowns in the discharge chamber did not exceed 120 μs. The results of measurements of the internal resistance of the batteries and its changes during operation are presented.

GaP as well as GaAs has face-centered cubic crystal phase at standard conditions. Despite it, GaP and GaAs nanowires frequently grow in a metastable hexagonal crystal phase called wurtzite. In this work, stable growth of GaP nanowire in the metastable phase is explained by accounting the elastic strain in the nucleus of a new layer. Crystal phase switch in heterostructured Ga(As,P) nanowire caused by heterointerface was studied theoretically and experimentally. Length of wurtzite segment after the switch of crystal phase linearly increases with nanowire diameter. Such dependence can not be explained by only kinetically driven effects. We consider such dependence as an evidence of elastic strain stabilization of the metastable phase in nanowires.

The mechanism of the azeotropy phenomenon has been established at a molecular level for the first time on the example of the HCOOH–H2O system, which has an azeotropic region. The studies are based on the regularities of the formation of heteroassociates with strong hydrogen bonds in binary systems and on the assumption that both phases of a boiling azeotropic mixture are composed of the same heteroassociates. It has been established that an aqueous formic acid solution is azeotropic if the heteroassociates composing this solution at room temperature are converted under heating into the most stable of possible heteroassociates 2НСООН ∙ 2Н2О and 2НСООН ∙ Н2О, which are retained at boiling temperature. Such restructuring in the solution leads to the maximum strengthening of intermolecular interactions and occurs with minimum energy expenditures.

The influence of the adjacent layers (SiO2, Al, Ni, Ti, W, TiN, TiN/W) on the crystallization kinetics of Ge2Sb2Te5 thin films was investigated using the techniques based on the application of two different methods—differential scanning calorimetry and measurements of the resistivity temperature dependences. Thin films were deposited by the magnetron sputtering. The composition of the films was determined by the Auger spectroscopy and was close to Ge2Sb2Te5. X-ray diffraction was used to investigate the structure of thin films and showed that the as-deposited films were in an amorphous state, while heat treatment at 250 °C for 30 min led to the crystallization to the cubic (rock salt) phase. Effective activation energy of crystallization obtained by differential scanning calorimetry at the beginning of the crystallization was 1.8 eV and then slightly decreased to 1.7 eV at the end of the process. The values of the effective activation energy obtained from the measurements of the resistivity temperature dependences were in the range of 2.5–2.9 eV at the beginning and in the range of 2.2–3.5 eV at the end of the crystallization process. The difference in the effective activation energies of crystallization for the GST225 thin films deposited on the different sublayers is caused by the influence of the neighboring sublayers on the crystallization process. It was found that crystallization temperatures correlate with the effective activation energies and increase with their growth.

Unique sulfur- and carbon- doped silicon nanoparticles, as well as partially oxidized, are obtained by nanosecond laser ablation of silicon in liquid carbon disulfide. Detailed structural, chemical, and optical characterization of these particles was performed by scanning and transmission electron microscopy, IR spectroscopy, energy dispersive X-ray spectroscopy, and Raman scattering spectroscopy. It is shown that the sulfur concentration in particles is on the order of 1 at %, owing to which they demonstrate a considerable absorption in the mid-IR region.

Gallium-nitride nanorods with a diameter of 15–40 nm and length of 50–150 nm are synthesized in monodisperse spherical mesoporous silica particles (MSMSPs) by high-temperature annealing of the Ga2O3 precursor in ammonia. The template material (a-SiO2) is selectively removed by etching the composite MSMSP/GaN particles with HF to give individual GaN nanorods. It is shown that the size of the GaN nanorods substantially exceeds the pore size of the MSMSPs (diameter ~3 nm, length ~10 nm). A possible mechanism by which GaN nanorods are formed is proposed. Redistribution of the material within the composite MSMSP/GaN particles possibly occurs via the surface diffusion of gaseous molecules within mesopores and via the diffusion of Ga and N atoms in a-SiO2.

A method for simple and fast (30–60 s) synthesis of spherical “Fe3O4 core–carbon shell” structures by atmospheric pressure aerosol pyrolysis of benzoic acid in dimethylformamide solutions containing dispersed Fe3O4 nanoparticles is described. It has been experimentally shown that it is possible to control both the size of the core–shell particles and the size of Fe3O4 grains and their amount in the particle core by the variation of benzoic acid concentration in solution and using pre-stabilized by mannitol iron oxide nanoparticles. It has been found that particles with an average size of 250–350 nm are formed at the concentration of benzoic acid in the range 0.5–1 mol/L. At a concentration of about 1 mol/L, preliminary stabilization of iron oxide nanoparticles by mannitol with a size of about 180 nm is performed.

Subject and Purpose. Peculiarities of the electromagnetic wave scattering at screens perforated by U-shaped slots are the subject of the paper. Numerical modeling of frequency-selective surfaces with frequency characteristics given and research into the possibilities of the performance control of the screens by complicating their elementary cell geometry are the purposes of the paper. Method and Methodology. The numerical modeling is performed upon the MWD3 software package developed in the laboratory of computational electromagnetics of the IRE NASU. Based on the scattering mode technique and the mode-matching technique taking into account the electromagnetic field behavior near the edges, this software package enables calculations of scattering characteristics of both compound waveguides and gratings with piece-wise boundaries. Results. A virtual waveguide was incorporated into the MWD3 projection schemes, extending capabilities of the MWD3 software and making it possible to treat the frequency-selective surfaces with piece-wise boundaries without adding new building blocks. Numerical modeling of perforated screens with U-shaped slots was carried out. Conclusion. Configurations of single and double metal screens and, also, a compound grating formed by two screens separated by a dielectric layer were calculated in full agreement with the given task. The perforated screens provide essential reflectivity decrease at low frequencies and, also, a low insertion loss level in the given millimeter wave region. The obtained results can be of interest for specialists in antenna-feeder engineering and for MWD3 software users.

Semiconductor nanowires exhibit numerous capabilities to advance the development of future optoelectronic devices. Among the III-V material family, gallium phosphide (GaP) is an attractive platform with low optical absorption and high nonlinear susceptibility, making it especially promising for nanophotonic applications. However, investigation of single nanostructures and their waveguiding properties remains challenging owing to typically planar experimental arrangements. Here we study the linear and nonlinear waveguiding optical properties of a single GaP nanowire in a special experimental layout, where an optically trapped structure is aligned along its major axis. We demonstrate efficient second harmonic generation in individual nanowires and unravel phase matching conditions, linking between linear guiding properties of the structure and its nonlinear tensorial susceptibility. The capability to pick up single nanowires, sort them with the aid of optomechanical manipulation and accurately position pre-tested structures opens a new avenue for the generation of optoelectronic origami-type devices.

We fabricated indium gallium nitride (InGaN) red light-emitting diodes (LEDs) with a peak emission wavelength of 649 nm and investigated their electroluminescence (EL) properties. An additional separated peak in the EL spectrum of the red LEDs at 20 mA was observed at 465 nm. This additional peak also exhibits a blue-shift with increasing currents as does the main emission peak. Using high-resolution microscopy, we observed many point-like emission spots in the EL emission images at the currents below 1 mA. However, these emission spots cannot be identified at currents above 5 mA because the red emission from quantum wells (QWs) is much stronger than that emitted by these spots. Finally, we demonstrate that these emission spots are related to the defects generated in red QWs. The measured In content was lower at the vicinity of the defects, which was regarded as the reason for separated short-wavelength emission in red InGaN LEDs.

In this study, the magnetic properties of magnetosomes isolated from lyophilized magnetotactic bacteria Magnetospirillum caucaseum SO-1 were assessed for the first time. The shape and size of magnetosomes and cell fragments were studied by electron microscopy and dynamic light scattering techniques. Phase and elemental composition were analyzed by X-ray and electron diffraction and Raman spectroscopy. Magnetic properties were studied using vibrating sample magnetometry and electron paramagnetic resonance spectroscopy. Theoretical analysis of the magnetic properties was carried out using the model of clusters of magnetostatically interacting two-phase particles and a modified method of moments for a system of dipole–dipole-interacting uniaxial particles. Magnetic properties were controlled mostly by random aggregates of magnetosomes, with a minor contribution from preserved magnetosome chains. Results confirmed the high chemical stability and homogeneity of bacterial magnetosomes in comparison to synthetic iron oxide magnetic nanoparticles.

III–V/Si integration is one of the bottlenecks of modern semiconductor technology. Dilute nitride phosphides (III–P–N) are among the promising materials providing lattice matching with Si. In this work, we study the effect of growth conditions on the chemical composition and properties of GaP1−xNx/GaP/Si planar heterostructures synthesized by plasma assisted molecular beam epitaxy. A series of samples with a maximum fraction of incorporated nitrogen as high as 5.05% is synthesized. The morphological, structural and optical properties of the heterostructures are studied. The tendency towards 3D growth and microtwinning in dilute nitride layers are demonstrated with the increase of nitrogen content. The most intense room temperature (RT) red photoluminescence (PL) emission is obtained with the sample containing 3.07% N. The PL intensity is found to be dependent on the N growth flux while its content only slightly changes with the flux. A low temperature PL study demonstrates efficient donor–acceptor recombination in the synthesized samples. Despite low structural perfection, the sample with the highest nitrogen content demonstrates PL response at RT centered at 1.76 eV.

Colloidal nanocrystals of AgInS2 were synthesized in aqueous solution using L-glutathione as a ligand. Wider bandgap semiconductor ZnS shell was deposited on the nanocrystal cores in order to enhance luminescence properties and stability. Thus prepared nanocrystals generally had an asymmetric multiple band emission spectrum. Variation of cation ratio [Ag+] to [In3+] led to a variation in the spectrum so that raising indium content caused an intensity increase of longer wavelength emission band. Photoluminescence and absorption spectroscopies, transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy were used for the sample characterization.

Glass formation in the AlCl–(CH3)2SO–H2O system was detected for the first time, the boundaries of the glass formation region were determined, and glass AlCl3 · 2.9(CH3)2SO · 4.8H2O was synthesized. The IR spectra of glass-forming solutions within the boundaries of the glass formation region and the glass AlCl3 · 2.9(CH3)2SO · 4.8H2O were recorded. It was concluded that (CH3)2SO enters the first coordination sphere of the aluminum ion through the oxygen atom. The glass AlCl3 · 2.9(CH3)2SO · 4.8H2O was studied by calorimetry, and its glass transition temperature was determined to be Tg = –32.3°C.

In the context of rising energy costs and the need to use new energy sources, works aimed at raising the surface temperature of heat radiators with reduced energy consumption are of particular importance, and it is especially important if these processes are also accompanied by the effects of self-stabilization. Bulk materials do not possess these properties. However, materials whose dielectric matrix is also an active element can provide up to 10 - 30% of the thermal energy that will be released in the material, thereby increasing the surface temperature and without increasing energy consumption. Therefore, the study of composite materials with different matrices is relevant. This article the influence of the matrix material on the electrical properties of composite materials was examined. It was established that the microstructure morphology of resistive materials changes significantly depending on the matrix type. In composites based on matrix AlN, for the entire range of concentrations HfC, conducting cluster is formed with a metallic conductivity. For composite systems Al2O3-HfC and Si3N4-HfC thermoactivated hopping conduction between nearest neighboring states observed. Thus, for materials based on Si3N4 matrix at temperatures up to 300°C observed reduction of charge carriers concentration with increasing temperature. The approximation of the temperature dependence of the electrical conductivity was carried out on the basis of the following possible variants of the nature of the electrical conductivity, namely: jump conductivity (nonlocalized states, localized states in the tails of conduction and valence bands, localized states near the Fermi level), tunneling. It can be assumed that the formation of conductive clusters occurred under the influence of two factors: magnetic field and mechanical loading. When using the AlN matrix, the influence of the magnetic field on the structure formation is smallest. This conclusion can be drawn from the fact that the formed conductive clusters have the appearance of a linear chain structure.

The regularities of mechanical activation (MA) and the reactivity of an high-energy 15Al + 85Bi2O3 (wt %) system have been studied with the use of X-ray diffraction analysis, synchronous thermal analysis, and the measurement of the ignition temperature upon the contact with a hot surface. For the nonactivated system, the intercomponent interaction has not been recorded upon their heating in a DSC cell up to 760°C. When MA is carried out, the reaction partly occurs directly in the course of grinding and upon the subsequent heating. In the course of heating at a rate of 10°C/min, the intercomponent interaction proceeds to yield Bi metal and amorphous Al2O3 in a temperature range of 350–800°C, with maxima being observed at 520 and 630°C. At temperatures below 480°C, the reaction occurs in nanolayers, as is evident from the position and shape of the melting curve obtained for formed bismuth. The effects of the duration of MA on the conversion of the components, reaction kinetics upon heating in the DSC cell, the temperature of ignition upon the contact of an activated sample with a hot surface, and the rate of mixture combustion have been determined. The optimal duration of MA, at which the ignition temperature is minimum, has been found.

Monodisperse spherical nanoporous silicon (np-Si) particles of submicrometer size are fabricated with mesoporous silica particles as a template. Silicon is synthesized within the mesopores of monodisperse silica particles by the thermal decomposition of monosilane. Then, the template material (a-SiO2) is removed by wet etching. The particles obtained have a small root-mean-square size scatter (no more than 10%) and large specific surface area (250 m2 g–1) and pore volume (0.5 cm3 g–1). It is shown that np-Si particles exhibit photoluminescence in the visible and near-IR (infrared) spectral ranges.

The heterocyclic polymer network nanocomposites obtained from bisphtalonitrile and various (from 0.03 to 5 wt %) modified silicate montmorillonite (MMT) nanolayers are studied. The nanostructure together with thermal, relaxation, and elastic properties of the composites are characterized with transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDXS), dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA). DMA and TGA measurements were performed in air and nitrogen mediums in the temperature range from 20 to 600–900°C. There was a various degree of exfoliation of MMT in the matrix to form single nanolayers, as well as thin and “thick” packs of MMT nanolayers, depending on its amount. We showed that there are strong constraining dynamics effects of the matrix by nanoparticles and sharp dynamic heterogeneity in the glass transition. We found that there are possibilities of complete suppression of the latter and of preservation of elastic characteristics of the composites unchanged at the temperatures from 20 to 600°C. The nanocomposites exhibit uniquely high thermal properties. A glass transition temperature of 570°C and satisfactory thermal stability are achieved with preservation of integrity of the material up to ~500°C in air and up to ∼900°C in nitrogen.

The results of studies of the structural and optical properties of two-dimensional GaSe layers grown by molecular-beam epitaxy on GaAs(001) and GaAs(112) substrates using a valve cracking cell for the Se source are reported. The influence of the MBE growth parameters (the substrate temperature, Ga flux intensity, Se/Ga incident flux ratio) on the surface morphology of the layers is studied. By means of transmission electron microscopy, electron diffraction technique, and Raman spectroscopy, it is shown that the structure of the GaSe layers corresponds to the γ-GaSe polytype. From X-ray diffraction analysis, it is established that there exist α-Ga2Se3 inclusions in the GaSe layers grown under conditions of high enrichment of the growth surface with Se.

Hybrid nanocomposites based on heterocyclic network, obtained from bisphenol A based phthalonitrile (BAPhN) with different (0.03–5.0 wt%) contents of reactive amino-montmorillonite (MMT) nanolayers, were synthesized and studied for the first time. Their structure, dynamics, thermal, relaxation and elastic properties were characterized using transmission electron microscopy (TEM), mid-infrared (mid-IR), far-infrared (far-IR) and energy dispersive X-ray (EDX) spectroscopies, differential scanning calorimetry (DSC), and by dynamic mechanical analysis (DMA) and thermogravimetry (TGA) measurements performed in both air and nitrogen mediums at temperatures from 20 to 600–900 °C. Depending on nanofiller content, different extents of MMT stacks exfoliation, from single nanolayers to MMT stacks with tens nanolayers-thickness, are observed in the nanocomposites. The pronounced dynamic heterogeneity in the glass transition and the ‘constrained dynamics’ effects are shown. For the pristine matrix, Tg (DMA) = 446 °С varying from 460 to 570 °С for the nanocomposites. After high-temperature treatment in N2 medium, the relaxation spectrum and glass transition disappear, and constant dynamic modulus E′ ≈ 3 GPa at 20–600 °С is registered. A satisfactory thermal stability of the nanocomposites, with retaining the sample integrity is observed at temperatures up to ~500 °C in air and up to 900 °C in N2 medium.

III–V planar semiconductor heterostructures based on GaPN alloy with a nitrogen concentration up to 2.12% were grown on Si(001) by plasma assisted molecular beam epitaxy. Dependence of nitrogen incorporation on the growth conditions and its effect on the crystal structure were investigated via analysis of X-ray diffraction, transmission electron microscopy, and Raman spectroscopy data. Continuous redshift and a substantial increase in intensity of the photoluminescence emission spectra were observed upon increase of nitrogen content. The effect of antiphase disorder in GaP buffer on the GaPN epilayer properties was studied. It was found that antiphase boundaries, protruding from the GaP/Si to the GaPN/GaP heterointerface, change their orientation and self-annihilate in the dilute nitride layer even with a low (0.5%) nitrogen content.

The electronic properties of semiconductor AIIIBV nanowires (NWs) due to their high surface/volume ratio can be effectively controlled by NW strain and surface electronic states. We study the effect of applied tension on the conductivity of wurtzite InxGa1–xAs (x ∼ 0.8) NWs. Experimentally, conductive atomic force microscopy is used to measure the I–V curves of vertically standing NWs covered by native oxide. To apply tension, the microscope probe touching the NW side is shifted laterally to produce a tensile strain in the NW. The NW strain significantly increases the forward current in the measured I–V curves. When the strain reaches 4%, the I–V curve becomes almost linear, and the forward current increases by 3 orders of magnitude. In the latter case, the tensile strain is supposed to shift the conduction band minima below the Fermi level, whose position, in turn, is fixed by surface states. Consequently, the surface conductivity channel appears. The observed effects confirm that the excess surface arse...

Spherical micro-mesoporous silicon (mSi) particles were fabricated by thermal decomposition of monosilane (SiH4) within the mesopores of monodisperse silica particles (MSP) and subsequent etching out of the template material. The thermal destruction of SiH4 occurs within the whole pore volume uniformly because in the thermal chemical vapor deposition method we developed, the limiting stage of the process in which MSP pores are filled with silicon is the reaction in which monosilane is decomposed, rather than its diffusion within template mesopores. The porosity of the mSi particles synthesized can be varied without changes in the shape and outer diameter of the particles by varying the parameters of the technological process of silane decomposition. The particles have large Brunauer-Emmett-Teller specific surface area (250–350 m2 g−1) and pore volume (0.3–0.5 cm3 g−1). For the first time the obtained submicron spherical porous silicon particles are monodisperse with a size scatter not exceeding 10%, which provides the identity of their hydrodynamic and adsorption properties so important for biomedical applications. We introduced the cytostatic drug doxorubicin (DOX) into mSi pores by the physical adsorption method. It was shown that DOX is desorbed from the mSi pores and penetrates into K-562 cancer cells, with local DOX concentration maxima observed in the intracellular space. The cytotoxicity of the mSi and mSi/DOX particles was studied, and the inhibition capacities of the cancer-cell proliferation by doxorubicin adsorbed by mSi particles and a DOX solution were compared in vitro. It was shown that the half-maximal inhibitory concentration (IC50) is four times lower under the action of DOX-loaded mSi particles as compared with free doxorubicin.

Multigraphene films have been for the first time obtained on the surface of quartz glass via carbonization of polyimide Langmuir–Blodgett films. The Raman spectra of the films show bands G and D and a broad band at 2300–3200 cm–1, which are characteristic of graphite-like films. The transmission electron microscopy demonstrated that the films are constituted by “stacks” of layers spaced by 0.36 nm. The surface resistance of the 5-nm-thick films was 1.2 ± 0.2 kΩ, and the transmittance was 87% at λ = 550 nm. The transmittance was 97% in the IR part of the spectrum and 70–80% in the UV part.

The study of the lanthanide ion luminescence as a function of their environment in polymer-inorganic composites is necessary for better understanding of the electron energy transfer processes in a condensed state. From a practical point of view, these materials are promising for optics and medicine. The nanoparticles of ZrO2-LnO1.5 (Ln = Eu, Tb) solid solutions were synthesized by hydrothermal method. The surface functionalization of the obtained nanoparticles by vinyl groups was carried out using 3-(trimethoxysilyl)propyl methacrylate. Soluble and cross-linked composites based on poly(methyl methacrylate) with ZrO2-LnO1.5 nanoparticles were synthesized using radical polymerization in solution and bulk. Molecular weight, thermal stability, and microhardness of the obtained composite materials were determined. The influence of both the polymerization conditions and the forming composite structure on the lanthanide ion photoluminescence in ZrO2 nanoparticles covalently bonded to the polymer matrix was studied. The combination of ZrO2-EuO1.5 and ZrO2-TbO1.5 nanoparticles in the poly(methyl methacrylate) resulted in the production of composites with photoluminescence spectra overlapping the red and green regions of the visible range. It was shown that the structure of the composite affects the absorbing capacity of luminescent centers and allows shifting the excitation spectrum in the longer wavelength region.

A series of phthalonitrile nanocomposites, obtained from bisphenol A based bisphthalonitrile (BAPhN) with 0.5 wt.% of different reactive amino- or epoxy-functionalized polyhedral oligomeric silsesquioxane (POSS) nanoparticles or montmorillonite (MMT) nanolayers, were synthesized and studied in detail. Their structure, dynamics and properties were characterized by TEM, mid-IR, far-IR and EDX spectroscopies, DSC, and by DMA and TGA measurements performed in air and N2 atmosphere at temperatures from 200 to 600–700 °C. Predominance of phthalocyanine macrocycles in the nodes of the matrix network is suggested; a satisfactory dispersion and a quasi-regular distribution of POSS nanoparticles have been revealed. For post-cured nanocomposites, DMA demonstrated an anomalous (“quasi-phase”) glass transition, dynamic heterogeneity in this transition, and “constrained dynamics” effects. Tg (DMA) was found to vary from 4600 to 560°С. After a high-temperature treatment in N2 atmosphere, disappearance of relaxation spectrum and glass transition as well as the constancy of the nanocomposite modulus E’≈ 3.2 GPa at 20–600°С were observed. A relatively satisfactory thermal stability of the nanocomposites was registered at temperatures up to ∼500 °C in air and 700 °C in N2.

Light-emitting organic field-effect transistors (LE-FETs) on the basis of composite films that consist of perovskite nanocrystals (CsPbBr3) embedded in a matrix of conjugated polymer—polyfluorene (PFO)—have been obtained, and their electrical and optical properties have been investigated. Output and transfer current-voltage characteristics (I-Vs) of FETs based on PFO : CsPbBr3 films (component ratio 1 : 1) have a slight hysteresis at temperatures of 100–300 K and are characteristic of hole transport. The hole mobility is ∼3.3 and ∼1.9 cm2/(V s) at the modes of the saturation and low fields, respectively, at 250 K and reaches ∼5 cm2/(V s) at 100 K. It has been shown that the application of pulsed voltage to LE-FETs based on PFO : CsPbBr3 can reduce the ionic conductivity and provide electroluminescence in this structure at 300 K.

Tailorable synthesis of III-V semiconductor heterostructures in nanowires (NWs) enables new approaches with respect to designing photonic and electronic devices at the nanoscale. We present a comprehensive study of highly controllable self-catalyzed growth of gallium phosphide (GaP) NWs on template-free silicon (111) substrates by molecular beam epitaxy. We report the approach to form the silicon oxide layer, which reproducibly provides a high yield of vertical GaP NWs and control over the NW surface density without a pre-patterned growth mask. Above that, we present the strategy for controlling both GaP NW length and diameter independently in single- or two-staged self-catalyzed growth. The proposed approach can be extended to other III-V NWs.

Laser-induced periodic surface structures (LIPSS) can be fabricated in virtually all types of solid materials and show great promise for efficient and scalable production of surface patterns with applications in various fields from photonics to engineering. While the majority of LIPSS manifest as modifications of the surface relief, in special cases, laser impact can also lead to periodic modulation of the material phase state. Here, we report on the fabrication of high-quality periodic structures in the films of phase-change material Ge2Sb2Te5 (GST). Due to considerable contrast of the refractive index of GST in its crystalline and amorphous states, the fabricated structures provide strong spatial modulation of the optical properties, which facilitates their applications. By changing the excitation laser wavelength, we observe the scaling of the grating period as well as transition between formation of different types of LIPSS. We optimize the laser exposure routine to achieve large-scale high-quality phase-change gratings with controllable period and demonstrate their reversible tunability through intermediate amorphization steps. Our results reveal the prospects of fast and rewritable fabrication of high-quality periodic structures for photonics and can serve as a guideline for further development of phase-change material-based optical elements.

Control and analysis of the crystal phase in semiconductor nanowires are of high importance due to the new possibilities for strain and band gap engineering for advanced nanoelectronic and nanophotonic devices. In this letter, we report the growth of the self-catalyzed GaP nanowires with a high concentration of wurtzite phase by molecular beam epitaxy on Si (111) and investigate their crystallinity. Varying the growth temperature and V/III flux ratio, we obtained wurtzite polytype segments with thicknesses in the range from several tens to 500 nm, which demonstrates the high potential of the phase bandgap engineering with highly crystalline self-catalyzed phosphide nanowires. The formation of rotational twins and wurtzite polymorph in vertical nanowires was observed through complex approach based on transmission electron microscopy, powder X-ray diffraction, and reciprocal space mapping. The phase composition, volume fraction of the crystalline phases, and wurtzite GaP lattice parameters were analyzed for the nanowires detached from the substrate. It is shown that the wurtzite phase formation occurs only in the vertically-oriented nanowires during vapor-liquid-solid growth, while the wurtzite phase is absent in GaP islands parasitically grown via the vapor-solid mechanism. The proposed approach can be used for the quantitative evaluation of the mean volume fraction of polytypic phase segments in heterostructured nanowires that are highly desirable for the optimization of growth technologies.

The LEDs were obtained that the peak emission wavelength and FWHM were 665 nm and 67 nm at 20 mA, respectively. It exhibited a large blueshift of the EL peak wavelength from 691 nm at 5 mA to 631 nm at 100 mA. In this range, the blue-shifted value was 60 nm. Besides, we realized the single peak emission LEDs without an additional emission. We obtained a light output, forward voltage, and EQE of 0.07 mW, 2.45 V, and 0.19% at 20 mA, respectively. The LEDs exhibited the temperature stability of EL intensity and peak wavelength.

We obtained the EL intensity enhancement by a factor of 1.3 with increasing of n-GaN thickness from 2 to 8 µm. We achieved a light output, forward voltage, FWHM and external quantum efficiency of 0.64 mW, 3.3 V, 59 nm, and 1.6% at 20 mA, respectively. Particularly, the wall plug efficiency was 1.0%, which is comparable with the state-of-the-art InGaN-based red LEDs. The reduction of the in-plane compressive stress by the GaN underlying layers appears to be crucial for enhancing the light output of InGaN-based red LEDs on conventional sapphire substrates.